<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>localStorage</title>
</head>
<body>
    <h2>localStorage</h2>
    <button onclick="saveData()">点我保存一个数据</button>
    <button onclick="readData()">点我读取一个数据</button>
    <button onclick="deleteData()">点我删除一个数据</button>
    <button onclick="deleteAllData()">点我清空所有数据</button>

    <script type="text/javascript">
        let P = {name:'zhangsan',age:'18'}

        function saveData(){
            localStorage.setItem('msg','hello')
            localStorage.setItem('msg2',666)
            localStorage.setItem('person',JSON.stringify(P))
        }

        function readData(){
            console.log(localStorage.getItem('msg'))
            console.log(localStorage.getItem('msg2'))
            const result = localStorage.getItem('person')
            console.log(JSON.parse(result))

            // 读取一个未存的数据  打印出来为 null   JSON.parse(null)==null
            console.log(localStorage.getItem('msg3'))  //null
            console.log(JSON.parse(localStorage.getItem('msg3'))) //null
            
        }

        function deleteData(){
            localStorage.removeItem('msg2')
        }

        function deleteAllData(){
            localStorage.clear()
        }
        
    </script>
</body>
</html>